In a conventional art, cooling a heat-generating element like a semiconductor device has been performed in such a manner that such heating element is mounted on a heat absorption block having good heat conduction and a plurality of heat pipe type cooling systems are installed thereon for cooling thereof and consequently the heat-generating element. The condenser section of the heat pipe is often used with multiple heat radiating fins attached thereon to accelerate condensation.
JP 3700870 B2 has described a heat pipe type cooler. The cooler described therein has a loop-shaped heat pipe, or an approximately U-shaped heat pipe, installed on a heat absorption block, wherein the lengths of the opposing two condenser sections of the U-shape are equal each to the other. The cooler offers good heat exchange efficiency since a part of the heat pipe is formed in a style of a horizontal heater. However, there is a problem in this art. When water for example is used as the working fluid of the heat pipe, the water inside the heat pipe freezes where the ambient temperature is below 0° C. Under this condition consequently, two opposing condenser sections of equal length on the heat pipe do not fully function causing the temperature of the semiconductor device to become possibly in excess of the specified permissible operating temperature.
JP 02-229455 A has described an apparatus of heat pipe system having a plurality of rod-shaped heat pipes filled with different types of working fluid. The heat pipes are divided into groups of two or more and each of the heat pipes in a group is filled with different working fluid particular to the group. For example, where the heat pipes in one group are filled with Furon R-113 as the working fluid and the heat pipes in other group with water, the system works well even at low temperatures because Furon R-113 does not freeze at the ambient temperature of 0° C. or lower. Further, this arrangement enables the heat pipe system to offer a high performance at usual operating temperatures.
JP 3020790 B2 has described a heat pipe type cooling device having a plurality of rod-shaped heat pipes. The heat pipes are divided into groups of two or more and each of the heat pipes in a group is given different pipe lengths, or is attached with differently arranged heat radiating fins particular to the group. The long heat pipes are attached with heat radiating fins in a number larger than that of the short heat pipes; therefore, they have a greater cooling capacity. Even at low temperatures, the short heat pipe still works as a heat pipe enabling a heat-generating element to be cooled, although the working fluid in the long heat pipe freezes at such temperatures.